524 ADVENTURES IX RADIOISOTOPE RESEARCH 



3 minutes after the injection of the labelled blood into the jugular vein, a few 

 cc. of blood are taken from the carotis. Further samples are taken at later times. 

 The heparinized blood samples are centrifuged, the corpuscles are weighed and 

 brought into solution by wet ashing; subsequently, 80 mgm of sodium phosphate 

 are added, and the phosphate content of the solution is precipitated as ammonium 

 magnesium phosphate. The standard samples are treated in a similar way. In 

 view of the much larger activity of the standard samples, only ^j^^ of the solution 

 obtained after ashing the sample is precipitated. 



Let us denote the amount of corpuscles injected into the rabbit by A, the ratio 

 of the activity of 1 gm corpuscles of the blood injected and of the activity of 1 gm 

 corpuscles secured from the circulation after the injection as B, then the total 

 amount of the corpuscles present in the circulation (X) is given by 



X— A- B. 



In some of our experiments, we used ^^P prepared from carbon disulfide which 

 was previously irradiated by a neutron beam. Should some of the ^^p present 

 in the solution obtained by the extraction process be adsorbed by colloidal par- 

 ticles or be present in the solution in another not properly dissolved state, this 

 part of the ^-P will be found after centrifugiag the standard blood sample in the 

 fraction containing the erythrocytes, while in the circulation this part may be 

 taken up by the reticulo-endothehal cells. In order to avoid a possible error due 

 to such an effect, we did not add the ^^P directly to the blood to be investigated 

 but to a small blood sample which was centrifuged at once. The plasma of the last 

 mentioned sample containing ^sp was added to the blood to be shaken in the 

 thermostat. 



An alternative method is the following one. Labelled phosphate is administered 

 to a rabbit, the blood of which thus becomes labelled. Few cc. of the labelled 

 blood are introduced into the circulation of another rabbit after the lapse of several 

 hours. By this procedure the activation in vitro can be avoided. 



Is the Label of the Corpuscles Properly Conserved? 



The method described above is based upon the assumption that the 

 32P introduced into the corpuscles while the blood containing labelled 

 phosphate is shaken in the thermostat, is not given off during the experi- 

 ment. One might expect that after the introduction of active blood into 

 the inactive circulation, ^^P will leave the corpuscles and get replaced 

 by 2iP atoms of the plasma. Such a process, if taking place at a suffi- 

 cient rate, would clearly frustrate the application of the method. Since, 

 however, a mixing of the blood introduced into the circulation of the 

 rabbit with the circulating blood does not last more than some minutes 

 or less, the blood sample can be secured, for example 3, 5, 7, and 9 

 minutes after the injection took place. 



The loss of activity of the corpuscles in experiments in which active 

 corpuscles were shaken in the thermostat with inactive plasma for 

 12 min was found to amount to 1.5 per cent, only. (Cf. also Hahn 

 and Hevesy 1940). That a possible loss of the labelling ^ap by the cor- 

 puscles does not influence our results is also seen in Table 1, in which 



